Graduation Omar Karam: Rock Cutting The Egyptian Way

Graduation presentation of Omar Karam
Graduation presentation of Omar Karam

Egypt is a great nation when it comes to ancient engineering. No other country has such a concentration of impressive monuments and such an interesting history as over there. If you are not convinced that modern Egyptians are not capable of great engineering feats you are wrong. Last Monday, Omar Karam graduated at our R&D department of Damen Dredging Equipment1 on his thesis about ‘CSD Rock Cutting.’

Cutting processes have been extensively described by Sape Miedema in ‘The Delft Sand, Clay & Rock Cutting Model’2. Omar has been using the frame work of Miedema to make some useful tools for the estimation of the production of our dredging equipment in rock. In due time, you will find the results of his thesis in the online dredge selection tool ‘Sandy’. Omar’s curiosity and ingenuity does not end here. He will continue studying at a university, but I do hope to meet him again, as he would be a valuable asset for our dredging community. Keep an eye out for him.

Program structure diagram of cutting force calculations
Program structure diagram of cutting force calculations

His graduation brings me back to my first lessons in dredging technology at the Delft University of Technology by the illustrious professor de Koning. In a sense he was an old school engineer, who hammered it in to us that thinking is done by doing it with your hands3. Back than the Polytechnic School was just rebranded to University and he was mocking that as a university, we had to set the topics in a broader perspective. So, he started his introduction on cutting technology with some slides of the unfinished obelisk at Aswan4 as every aspect of the cutting process could be illustrated.

Phases of chip forming in rock cutting
Phases of chip forming in rock cutting

The story according to de Koning is: ‘Around the quarry of the obelisk, they have found diorites5. These are some sort of volcanic balls of rock. In combination with the marks and scratches all around the obelisk, archaeologists believe these stones have been used to pound the granite. The impact compresses the bedrock and the resulting stresses fracture the contact surface(1). For every hit a whiff of dust is created. Eventually the dust is collected and scooped away for the next layer. Next, trees would be planted in the trench on one side of the obelisk. The growing root system displaces volume and create shear stress underneath the obelisk that would sever the obelisk from the bed rock(2). At last the trees are removed and dry wooden dowels would have been inserted in the shear cracks. Saturating the wooden dowels will make them grow. The last strands of rock will now be broken due to tensile stresses(3). Repeated insertion of new dry dowels and saturating them will lift the whole obelisk enough to pull some ropes under and carry the obelisk away to the building site.’

Although the diorites and the scratch marks are a smoking gun, current archaeologists argue about the feasibility of this process as experiments yield a very low production and it is doubted that the obelisk could be finished in the lifetime of the client6. Even if disputed, de Koning told a story that conveys the message; I vividly remember it and makes me understand the rock cutting process.

These mysterious monolithic ornamental spires have been an inspiration for many legends and stories. When we have solved the riddle of the rock cutting with diorite balls, it may inspire the development of new rock cutting technology for the dredging community and we can put the story of the obelisks to an end.7

End of the story on the cutting of obelisks (Credit: Uderzo)
End of the story on the cutting of obelisks (Credit: Uderzo)

References

  1. Innovation, Damen
  2. The Delft Sand, Clay & Rock Cutting Model, TU Delft
  3. De Koning (1978), Denken met de handen’, TU Delft
  4. Unfinished obelisk, Wikipedia
  5. Diorite, Wikipedia
  6. The Unfinished Obelisk, NOVA
  7. Asterix and Cleopatra, Goscinny-Uderzo

See also

Lessons in Camping: Basic Soil Investigation

Pitching our tent at Bad Bear Campground, Idaho, USA

Oh the horror! An old salt like me had to go camping during our summer holiday. Our daughter had her birthday during our road trip in the USA and she wanted to celebrate it by camping in the woods. Complying to her wishes we pitched a tent and roasted marshmallows. Meanwhile my mind was frantically searching for familiar clues to connect to my maritime heritage. Hammering down the tent pegs, it dawned to me: putting up a tent is basically a simple Standard Penetration Test.

Standard Penetration Test explanation infographic

Standard Penetration Test is one of the easiest soil investigations you could do1. All you need is a pipe and a hammer. You count the number of blows to hammer the pipe down and you have an indication of the effort it takes to cut the soil. This method completely ignores sophisticated parameters as e.g. undrained shear strength, porosity or internal friction angle. It is very crude in its results. On the other hand, the basic principle of driving the pipe into the ground is very similar to the cutting action of the pick points on a cutter. As such, it is a very good indicator for the performance of a cutter head. This is also the reason, why for initial discussions about the performance of a CSD, the SPT is a good starting point to ask the client. He might have a report like this already available, or he can easily perform the tests. Also ‘Sandy’ accepts SPT values for an indication of the soil quality2.

Sandy’s soil parameter input page

Be aware, that SPT’s are often not very deep. Of course, a full soil investigation report with a Cone Penetration Test is much more valuable. We can always translate the results from a CPT report into a SPT value. But the SPT information is not covering all the parameters to translate this to a CPT. Sometimes even an SPT report fails. And then it might be useful to discuss with the client on a qualitative level about the soil condition. Usually people have actually touched the soil, or at least can paint a mental picture of the soil conditions and these criteria might help to use the same descriptive language.

Standardised qualitative description

Hammering a rod into the soil is a relative cheap and quick method to collect the soil consistency. It can be performed everywhere, anytime, under most conditions. That is why it was also selected for the soil investigation on one of the most remote locations imaginable. Although it is still on my wish list of dream destinations, the prohibitive price tag of the ticket will prevent it for me to pitch up my tent over there. I just have to revel in the camping adventures of Neil and Buzz.

Astronaut Edwin Aldrin takes a core-tube sample3 (Credit: NASA)

References

  1. ASTM: Standard Test Method for Standard Penetration Test
  2. Sandy, Dredge Finder
  3. Astronaut Edwin Aldrin takes a core-tube sample

See also